JP2017055589A - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To strengthen element protection while insulating the input and output, and while suppressing the circuit scale of a transforming power converter 20.SOLUTION: In a power converter 20, a first inverter circuit (e.g., constituted of a full-bridge circuit) 22 converts a DC voltage inputted via a reactor L, connected with a DC power supply 10, into an AC voltage while boosting. A transformer T transmits the output power from the first inverter circuit 22, provided on the primary, to the secondary. A second inverter circuit 23a is provided on the secondary of the transformer T, and converts an AC power, outputted from the first inverter circuit 22, into a DC power. A short circuit switch 21 short-circuits the opposite ends of the reactor L1.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a power conversion device that performs transformation while insulating input and output.

  An isolated boost converter is known as a high-efficiency and low-cost DC-DC converter circuit topology capable of performing isolation and boosting in one stage. In the isolated boost converter, on the primary side, a reactor is inserted between the DC power supply and the inverter circuit to provide a conduction period for the inverter circuit. When energy is stored in the reactor during this conduction period and the inverter circuit returns to the complementary operation, the energy is released and the boosted voltage is transmitted to the primary side of the transformer.

  When the load connected to the secondary side is removed, the power is turned off, or the like, the output current is suddenly lowered and a surge voltage is generated when a transition is made to a no load or light load state. In particular, in a current type isolated converter such as an isolated step-up converter, a large surge voltage is generated at both ends of the switching element due to leakage inductance of a high frequency transformer and release of magnetic energy remaining in the primary side reactor. As a countermeasure against the surge voltage caused by these, it is conceivable to provide a snubber circuit on the primary side (see, for example, Patent Document 1).

  However, when rapid load fluctuations (for example, full load on / off) frequently occur in a short time, the snubber circuit alone may not sufficiently absorb the surge voltage that occurs repeatedly. If the surge voltage cannot be sufficiently absorbed, a switching element (for example, an IGBT (Insulated Gate Bipolar Transistor)) that constitutes the inverter circuit may have a breakdown voltage, and the element may malfunction.

  By the way, in a DC-DC converter, it is necessary to suppress the inrush current which generate | occur | produces at the time of starting. In order to suppress the inrush current, a method of precharging a secondary capacitor connected in parallel with the load with a precharge circuit is conceivable (see, for example, Patent Document 2), but it is necessary to provide a precharge circuit separately. Circuit area and cost increase.

US Pat. No. 6,452,815 US Pat. No. 6,587,356

  The present inventor has found a circuit configuration that contributes to element protection from surge voltage and suppression of inrush current at start-up by adding a simple circuit to the isolated boost converter.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a power conversion device that transforms while insulating input / output, and provides a power conversion device with enhanced element protection while suppressing the circuit scale. There is.

  In order to solve the above-described problems, a power converter according to an aspect of the present invention includes a reactor connected to a DC power supply, and a first inverter that converts a DC voltage input through the reactor into an AC voltage while boosting the DC voltage. A circuit, a transformer for transmitting the output power of the first inverter circuit provided on the primary side to the secondary side, and an AC power provided on the secondary side of the transformer and output from the first inverter circuit for direct current A second inverter circuit for converting to electric power, and a short-circuit switch for short-circuiting both ends of the reactor.

  It should be noted that any combination of the above-described constituent elements and a representation of the present invention converted between a method, an apparatus, a system, and the like are also effective as an aspect of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, it is a power converter device which transforms, isolating input / output, Comprising: The power converter device with which element protection was strengthened, suppressing a circuit scale is realizable.

It is a figure for demonstrating the structure of the power converter device which concerns on Embodiment 1. FIG. It is a time chart for demonstrating the basic operation | movement of the power converter device of FIG. It is a time chart for demonstrating the operation | movement at the time of starting of the power converter device of FIG. FIG. 6 is a diagram for explaining a configuration of a power conversion device according to a second embodiment. It is a figure which shows the modification 1 of a short circuit switch. It is a figure which shows the modification 2 of a short circuit switch.

(Embodiment 1)
FIG. 1 is a diagram for explaining a configuration of a power conversion device 20 according to the first embodiment. The power conversion device 20 according to the first embodiment is a unidirectional insulation type DC-DC converter that converts DC power supplied from the DC power supply 10 into DC-DC and supplies the DC power to the DC load 30. The DC power source 10 corresponds to, for example, a storage battery, a solar cell, a fuel cell, or the like.

  A first smoothing capacitor C1 is connected in parallel with the DC power supply 10. For example, an electrolytic capacitor is used as the first smoothing capacitor C1. A reactor L1 is connected in series with the DC power supply 10. Inverter circuit 22 is connected to DC power supply 10 via reactor L1. The inverter circuit 22 converts the DC power input from the reactor L1 into AC power.

  In the present embodiment, the inverter circuit 22 includes a first leg in which the first switching element Q11 and the second switching element Q12 are connected in series, and a second leg in which the third switching element Q13 and the fourth switching element Q14 are connected in series. Are composed of a full bridge circuit connected in parallel. The midpoint of the first leg and the midpoint of the second leg are connected to both ends of the primary winding of the high-frequency transformer T, respectively.

  For example, IGBTs can be used for the first switching element Q11 to the fourth switching element Q14. The collector terminal of the first switching element Q11 and the collector terminal of the third switching element Q13 are connected to the positive electrode of the DC power supply 10 via the reactor L1. The emitter terminal of the second switching element Q12 and the emitter terminal of the fourth switching element Q14 are connected to the negative electrode of the DC power supply 10. The emitter terminal of the first switching element Q11 and the collector terminal of the second switching element Q12 are connected, and the emitter terminal of the third switching element Q13 and the collector terminal of the fourth switching element Q14 are connected.

  The first free-wheeling diode D11 to the fourth free-wheeling diode D14 are connected in reverse to the first switching element Q11 to the fourth switching element Q14, respectively. When MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) are used for the first switching element Q11 to the fourth switching element Q14, the first free-wheeling diode D11 to the fourth free-wheeling diode D14 are formed in the direction from the source to the drain. A parasitic diode can be used.

  The high-frequency transformer T converts the output voltage of the inverter circuit 22 connected to the primary winding in accordance with the turn ratio of the primary winding and the secondary winding, and outputs it to the rectifier circuit 23 connected to the secondary winding. To do. The rectifier circuit 23 rectifies the output power of the inverter circuit 22 input via the high frequency transformer T and supplies the rectified circuit to the DC load 30. The rectifier circuit 23 can be constituted by a diode bridge circuit, for example. In the example shown in FIG. 1, one end of the secondary winding of the high-frequency transformer T is connected to a node between the anode terminal of the first rectifier diode D15 and the cathode terminal of the second rectifier diode D16, and the other end of the secondary winding. Is connected to a node between the anode terminal of the third rectifier diode D17 and the cathode terminal of the fourth rectifier diode D18.

  The cathode terminal of the first rectifier diode D15 and the cathode terminal of the third rectifier diode D17 are connected to the positive terminal of the DC load 30, and the anode terminal of the second rectifier diode D16 and the anode terminal of the fourth rectifier diode D18 are connected to the DC load 30. Connected to the negative terminal. A second smoothing capacitor C3 is connected in parallel with the DC load 30. For example, an electrolytic capacitor is used as the second smoothing capacitor C3.

  The voltage detection unit 24 detects a voltage (a voltage across the second smoothing capacitor C3) output to the DC load 30 and outputs the detected voltage to the control unit 25. For example, a differential amplifier can be used for the voltage detection unit 24.

  The control unit 25 controls the entire power conversion device 20. The configuration of the control unit 25 can be realized by cooperation of hardware resources and software resources, or only by hardware resources. As hardware resources, analog elements, microcomputers, DSPs, ROMs, RAMs, FPGAs, and other LSIs can be used. Firmware and other programs can be used as software resources.

  The control unit 25 drives the inverter circuit 22 so that the output voltage of the power conversion device 20 maintains the target voltage. Specifically, the control unit 25 generates a PWM signal as a drive signal for the first switching element Q11 to the fourth switching element Q14, and supplies the PWM signal to the gate terminals of the first switching element Q11 to the fourth switching element Q14. The controller 25 can increase the output voltage of the power converter 20 by increasing the duty ratio of the PWM signal, and can decrease the output voltage of the power converter 20 by decreasing the duty ratio of the PWM signal. The control unit 25 compares the output voltage detected by the voltage detection unit 24 with the target voltage. If the detected output voltage is lower than the target voltage, the control unit 25 increases the duty ratio, and the detected output voltage is higher than the target voltage. If so, reduce the duty ratio.

  A snubber circuit is provided on the primary side to absorb the surge voltage. In the example shown in FIG. 1, an RCD snubber circuit is connected to the input side of the inverter circuit 22. Specifically, a snubber diode D3 and a snubber capacitor C2 are connected in series between the positive input terminal and the negative input terminal of the inverter circuit 22. The anode terminal of the snubber diode D3 is connected to the positive input terminal of the inverter circuit 22, the cathode terminal of the snubber diode D3 is connected to one end of the snubber capacitor C2, and the other end of the snubber capacitor C2 is connected to the negative input terminal of the inverter circuit 22. Is done. A node between the snubber diode D3 and the snubber capacitor C2 is connected to the positive terminal of the DC power supply 10 through the resistor R1. The resistor R1 consumes the energy stored in the snubber capacitor C2.

The surge voltage generated in the normal switching operation of the first switching element Q11 to the fourth switching element Q14 can be absorbed by the snubber capacitor C2. However, when the DC load 30 changes abruptly from a heavy state to a light state, the surge voltage may not be absorbed by the snubber capacitor C2. The surge voltage is mainly generated due to the energy accumulated in the leakage inductance L _L of the high-frequency transformer T and the energy accumulated in the reactor L1.

When the DC load 30 is operating at the maximum load, the rated current flows through the reactor L1, and a large amount of energy is accumulated. When the DC load 30 is removed from the state and the DC load 30 is turned off to switch to a no-load state, a large DC current flows from the reactor L1. To absorb all the DC current and the leakage inductance L snubber capacitor DC current from _L C2 from the reactor L1, it requires a large capacity capacitor. In that case, the circuit area and cost increase.

  As a countermeasure against this surge voltage, in the present embodiment, a short-circuit switch 21 for short-circuiting both ends of the reactor L1 is added. When the short-circuit switch 21 is in the ON state, the direct current accumulated in the reactor L1 flows back through the closed loop formed by the reactor L1 and the short-circuit switch 21, and energy is consumed by the resistance component on the closed loop. The resistance component is a resistance component included in each element and wiring on the closed loop.

  Short-circuit switch 21 blocks current from the input terminal of reactor L1 to the output terminal on the short-circuit path, and conducts current from the output terminal of reactor L1 to the input terminal in accordance with a drive signal from control unit 25. It is a reverse blocking switch that is non-conductive. In the example shown in FIG. 1, the short-circuit switch 21 is formed of a series circuit of a fifth rectifier diode D1 and a short-circuit switching element Q1. A first built-in diode D2 is connected in parallel with the short-circuit switching element Q1. When an IGBT is used for the short-circuit switching element Q1, the first built-in diode D2 is connected in the direction from the emitter to the collector of the IGBT. When a MOSFET is used for the short-circuit switching element Q1, a parasitic diode formed in the direction from the source to the drain can be used as the first built-in diode D2.

  In the example shown in FIG. 1, the cathode terminal of the fifth rectifier diode D1 is connected to the input terminal of the reactor L1, the anode terminal of the fifth rectifier diode D1 is connected to the emitter terminal or the source terminal of the short-circuit switching element Q1, The collector terminal or drain terminal of switching element Q1 is connected to the output terminal of reactor L1. In addition, as shown in FIG. 4 described later, the order of the fifth rectifier diode D1 and the short-circuit switching element Q1 may be reversed.

  FIG. 2 is a time chart for explaining the basic operation of the power conversion apparatus 20 of FIG. During normal operation of power conversion device 20, control unit 25 drives first switching element Q11 and fourth switching element Q14, and second switching element Q12 and third switching element Q13 in a complementary manner. At that time, the first switching element Q11 to the fourth switching element Q14 are all controlled to be in an ON state, and a period Tc for storing energy in the reactor L1 is provided. Next, when the first switching element Q11 to the fourth switching element Q14 return to the complementary operation, a voltage obtained by adding the voltage of the DC power supply 10 and the voltage accumulated in the reactor L1 (boosted voltage) is the primary winding of the high-frequency transformer T. Applied to the line. During normal operation, the control unit 25 controls the short-circuit switching element Q1 to be turned off.

  When the DC load 30 falls below a predetermined value, the control unit 25 controls the power conversion device 20 to be in a resting state. Whether or not the DC load 30 has fallen below a predetermined value can be determined by whether or not the voltage value detected by the voltage detection unit 24 has exceeded a predetermined voltage value for load drop detection. Note that a current detection unit (not shown) that detects an output current to the DC load 30 may be provided, and determination may be made based on whether or not the detected current has exceeded a predetermined current value for load reduction detection.

  In the resting state, the control unit 25 controls all of the first switching element Q11 to the fourth switching element Q14 to the off state and controls the short-circuit switching element Q1 to the on state. As a result, the reactor L1 is short-circuited, the current flowing through the reactor L1 flows into the short-circuit switch 21, and the magnetic energy remaining in the reactor L1 is consumed in a closed loop formed by the reactor L1 and the short-circuit switch 21. Therefore, the surge voltage resulting from the current flowing from reactor L1 is absorbed. The surge voltage resulting from the current flowing from the leakage inductance of the high-frequency transformer T is absorbed by the snubber capacitor C2. Accordingly, the first switching element Q11 to the fourth switching element Q14 are protected from the surge voltage.

  FIG. 3 is a time chart for explaining the operation at the time of startup of the power conversion device 20 of FIG. When the power conversion device 20 is started up, the control unit 25 short-circuiting switching element Q1 is controlled to be in an ON state, and the duty ratio of the first switching element Q11 to the fourth switching element Q14 is increased according to the voltage increase of the second smoothing capacitor C3. Gradually increase from zero. When the voltage of the second smoothing capacitor C3 exceeds the set voltage value Vth, the control unit 25 turns off the short-circuit switching element Q1.

  The set voltage value Vth is set to a voltage value at which an inrush current from the DC power supply 10 to the second smoothing capacitor C3 is suppressed. If the second smoothing capacitor C3 is precharged to a voltage close to the voltage applied from the primary side via the high-frequency transformer T, the inrush current to the second smoothing capacitor C3 at the time of activation can be suppressed. Accordingly, the set voltage value Vth is set to a value lower than the voltage value obtained by multiplying the voltage of the DC power supply 10 by the turn ratio of the high-frequency transformer T (the number of turns of the secondary winding / the number of turns of the primary winding). The constant value is preferably a very small value.

  In this way, the short-circuiting switching element Q1 is controlled to be in an ON state until the precharge up to the set voltage value Vth of the second smoothing capacitor C3 is completed, and the reactor L1 is short-circuited. As a result, reactor L1 is disabled, the reactor L1 and inverter circuit 22 no longer function as a boost converter, and inrush current can be prevented from flowing from the boost converter. Further, the inverter circuit 22 and the high frequency transformer T function as a step-down converter, and the second smoothing capacitor C3 can be charged from a voltage lower than the voltage of the DC power supply 10. As described above, the second smoothing capacitor C3 can be gently precharged (soft start) only by the switching operation of the first switching element Q11 to the fourth switching element Q14.

  As described above, according to the first embodiment, in the isolated boost converter, by providing the short-circuit switch 21 for short-circuiting the reactor L1, the first voltage included in the inverter circuit 22 from the surge voltage caused by the sudden load change is provided. The switching element Q11 to the fourth switching element Q14 can be protected. Since it is not necessary to use a high withstand voltage for the first switching element Q11 to the fourth switching element Q14, an increase in circuit area and cost can be suppressed.

  The short-circuit switch 21 also serves as a switch for invalidating the reactor L1 at the time of startup. By disabling reactor L1, second smoothing capacitor C3 can be gently precharged, and soft start can be realized. When the reactor L1 is in an effective state, it is difficult to gently precharge the second smoothing capacitor C3 via the inverter circuit 22 and the high frequency transformer T. In that case, it is necessary to separately provide another precharge circuit that does not pass through the inverter circuit 22 and the high-frequency transformer T, which increases circuit area and cost.

  The isolated boost converter can reduce the number of elements as compared with a general combination of a boost chopper and an inverter circuit. Therefore, according to the present embodiment, it is a power conversion device having an insulating action and a boosting action, and a power conversion device with enhanced element protection while suppressing the circuit scale can be realized.

(Embodiment 2)
FIG. 4 is a diagram for explaining the configuration of the power conversion device 20 according to the second embodiment. The power conversion device 20 according to the second embodiment is an insulated bidirectional DC-AC converter. Compared with the power conversion device 20 according to the first embodiment, the DC load 30 is replaced with the DC-AC converter 26 and the system 40, and the rectifier circuit 23 is replaced with the inverter circuit 23a.

  The secondary-side inverter circuit 23 a has the same configuration as that of the primary-side inverter circuit 22. That is, in the inverter circuit 23a, the first leg in which the fifth switching element Q21 and the sixth switching element Q22 are connected in series and the second leg in which the seventh switching element Q23 and the eighth switching element Q24 are connected in series are connected in parallel. It consists of a full bridge circuit. A fifth free-wheeling diode D21 through an eighth free-wheeling diode D24 are connected in reverse to the fifth switching element Q21 through the eighth switching element Q24, respectively. The midpoint of the first leg and the midpoint of the second leg are respectively connected to both ends of the secondary winding of the high-frequency transformer T.

  In FIG. 4, the primary-side snubber circuit is composed of an active clamp circuit. Specifically, the clamping switching element Q2 and the snubber capacitor C2 are connected in series between the positive input terminal and the negative input terminal of the inverter circuit 22. A second built-in diode D4 is connected in parallel with the clamp switching element Q2. When the IGBT is used for the clamp switching element Q2, the second built-in diode D4 is connected in the direction from the emitter to the collector of the IGBT. When a MOSFET is used for the clamp switching element Q2, a parasitic diode formed in the direction from the source to the drain can be used as the second built-in diode D4.

  The emitter or source terminal of the clamp switching element Q2 is connected to the positive input terminal of the inverter circuit 22, the collector terminal or drain terminal of the clamp switching element Q2 is connected to one end of the snubber capacitor C2, and the other end of the snubber capacitor C2. Is connected to the negative input terminal of the inverter circuit 22. The control unit 25 turns on the clamp switching element Q2 at a predetermined timing, and discharges the energy charged in the snubber capacitor C2 to the power supply line. Compared with the RCD snubber circuit shown in FIG. 1, the energy absorbed in the snubber capacitor C2 is regenerated without being consumed, so that energy loss can be reduced.

  The snubber circuit of the power conversion device 20 shown in FIG. 1 may be configured with an active clamp circuit, or the snubber circuit of the power conversion device 20 shown in FIG. 4 may be configured with an RCD snubber circuit. In each case, another type of snubber circuit may be used.

  The short-circuit switch 21 shown in FIG. 4 has the same order of operation as the fifth rectifier diode D1 and the short-circuit switching element Q1 in comparison with the short-circuit switch 21 shown in FIG.

  In the power conversion device 20 illustrated in FIG. 4, when the DC power supplied from the DC power supply 10 is converted to AC power and reversely flows into the system 40, the control unit 25 includes the fifth switching elements Q21 to Q21 included in the inverter circuit 23a. All the eighth switching elements Q24 are controlled to be turned off. As a result, the inverter circuit 23a has a circuit configuration similar to that of the rectifier circuit 23 including the diode bridge circuit shown in FIG. By regarding the DC-AC converter 26 and the system 40 as the direct current load 30 shown in FIG. 1, the description of the processing of the power conversion device 20 shown in FIG. 1 is directly applied to the processing of the power conversion device 20 shown in FIG. . An AC load may be connected to the AC side of the DC-AC converter 26 instead of the system 40.

  When the AC power supplied from the system 40 is converted into DC power and the storage battery as the DC power supply 10 is charged, the control unit 25 complements the fifth switching element Q21 to the eighth switching element Q24 included in the inverter circuit 23a. The first switching element Q11 to the fourth switching element Q14 included in the inverter circuit 22 are all controlled to be turned off. The control unit 25 may control the short-circuit switching element Q1 to the on state to bypass the reactor L1, or may control the short-circuit switching element Q1 to the off state and use the reactor L1 as a filter.

  As described above, according to the second embodiment, the same effect as that of the first embodiment is obtained even in the bidirectional insulated boost converter. In the second embodiment, an example of an insulated bidirectional DC-AC converter has been described. However, an insulated bidirectional DC-DC converter may be used. In this case, the DC-AC converter 26 and the system 40 in FIG. 4 are replaced with a DC power source. In in-vehicle applications, the auxiliary battery and the traveling battery may be connected via a bidirectional DC-DC converter, and the insulated bidirectional DC-DC converter according to the modification of the second embodiment is, for example, applicable to the application. Can be used.

  The present invention has been described based on the embodiments. The embodiments are exemplifications, and it will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are within the scope of the present invention. .

  In the first and second embodiments, the example in which the series circuit of the fifth rectifier diode D1 and the short-circuit switching element Q1 is used as the short-circuit switch 21 has been described. Other configurations are possible in this respect.

  FIG. 5 is a diagram illustrating a first modification of the short-circuit switch 21. Modification 1 is an example in which a reverse blocking IGBT (Q1a) is used as the short-circuit switch 21. The emitter terminal of reverse blocking IGBT (Q1a) is connected to the input terminal of reactor L1, and the collector terminal is connected to the output terminal of reactor L1. The reverse blocking IGBT (Q1a) is an element having a sufficient breakdown voltage performance with respect to the reverse bias voltage without connecting a reverse blocking series diode for reverse breakdown voltage protection.

  FIG. 6 is a diagram illustrating a second modification of the short-circuit switch 21. Modification 2 is an example in which a relay RY is used as the short-circuit switch 21. When an active clamp circuit is used for the snubber circuit, the discharge current does not flow into the input terminal side of the reactor L1 via the resistor R1 as in the case of using the RCD snubber circuit. Even if such a bidirectional switch is used, the return current of the reactor L1 is not affected.

  In the first and second embodiments described above, the example in which the full bridge circuit is used as the inverter circuit 22 has been described. However, a push-pull circuit may be used.

  The embodiment may be specified by the following items.

[Item 1]
A reactor (L1) connected to a DC power source (10);
A first inverter circuit (22) that converts a DC voltage input through the reactor (L1) into an AC voltage while boosting the DC voltage;
A transformer (T) for transmitting output power of the first inverter circuit (22) provided on the primary side to the secondary side;
A second inverter circuit (23a) that is provided on the secondary side of the transformer (T) and converts AC power output from the first inverter circuit into DC power;
A short-circuit switch (21) for short-circuiting both ends of the reactor (L1);
The power converter device (20) characterized by comprising.
According to this, by adding the short-circuit switch (21) in the isolated boost converter, it is possible to realize a circuit configuration that contributes to element protection from surge voltage and suppression of inrush current at startup.
[Item 2]
The first inverter circuit (22) includes a first leg in which a first switching element (Q11) and a second switching element (Q12) are connected in series, a third switching element (Q13), and a fourth switching element (Q14). ) Includes a full bridge circuit connected in parallel with a second leg connected in series,
The power converter (20)
A controller (25) for driving the first switching element (Q11) and the fourth switching element (Q14) and the second switching element (Q12) and the third switching element (Q13) in a complementary manner; Prepared,
When the first inverter circuit (22) is operated, the control unit (25) controls all of the first switching element (Q11) to the fourth switching element (Q14) to be in an on state so that the reactor (L1 The power converter device (20) according to item 1, characterized in that a period for storing energy is provided.
According to this, a DC voltage can be converted into an AC voltage while being boosted by the reactor (L1) and the full bridge circuit, and supplied to the primary winding of the transformer (T).
[Item 3]
The DC power output from the second inverter circuit (23a) is converted into AC power and supplied to the AC power supply (40) or the AC load, or the AC power supplied from the AC power supply (40) is converted into DC power. And a DC-AC converter that supplies the second inverter circuit (23a),
The controller (25) turns off the first switching element (Q11) to the fourth switching element (Q14) when the load seen from the AC side of the DC-AC converter (26) falls below a predetermined value. The power conversion device (20) according to item 2, wherein the power conversion device (20) is controlled to a state, and the short-circuit switch (21) is controlled to an on state.
By short-circuiting both ends of the reactor (L1) at the time of no load or light load, the first switching element (Q11) to the fourth switching element (Q14) are protected from a surge voltage generated when transitioning to no load or light load. can do.
[Item 4]
A capacitor (C3) provided in parallel on the DC side of the second inverter circuit (23a);
The control unit (25) controls the short-circuit switch (21) to be in an ON state when the power conversion device (20) is activated, and when the voltage of the capacitor (C3) exceeds a set value, the short-circuit switch (21) 21. The power conversion device (20) according to item 2 or 3, wherein 21) is controlled to an off state.
By controlling the short-circuit switch (21) to be in an on state at the time of startup, the reactor (L1) can be invalidated and soft start can be realized.
[Item 5]
When the power converter (20) is started, the control unit (25) is configured to switch the first switching element (Q11) to the fourth switching element (Q14) according to the voltage increase of the capacitor (C3). Item 5. The power conversion device (20) according to item 4, wherein the duty ratio is increased.
According to this, soft start can be realized without separately providing a precharge circuit for precharging the capacitor (C3).
[Item 6]
The short-circuit switch (21) blocks current from the terminal on the DC power supply (10) side of the reactor (L1) to the terminal on the first inverter circuit (22) side, and the first inverter circuit (22) The power conversion according to any one of Items 1 to 5, wherein the switch is a reverse blocking switch that conducts or non-conducts current from a terminal on the side to the terminal on the DC power supply (10) side according to a drive signal. Device (20).
According to this, the direct current remaining in the reactor (L1) can recirculate the closed loop without being inhibited.

10 DC power supply, 20 power converter, L1 reactor, C1 first smoothing capacitor, 21 short-circuit switch, D1 fifth rectifier diode, Q1 short-circuit switching element, D2 first built-in diode, R1 resistor, D3 snubber diode, C2 snubber capacitor 22 Inverter circuit, Q11 first switching element, Q12 second switching element, Q13 third switching element, Q14 fourth switching element, D11 first return diode, D12 second return diode, D13 third return diode, D14 fourth Freewheeling diode, L _L leakage inductance, T high frequency transformer, 23 rectifier circuit, D15 first rectifier diode, D16 second rectifier diode, D17 third rectifier diode, D18 fourth rectifier diode, C3 second smoothing diode Capacitor, 24 voltage detector, 25 controller, 30 DC load, Q2 switching element for clamping, D4 second built-in diode, 23a inverter circuit, Q21 fifth switching element, Q22 sixth switching element, Q23 seventh switching element, Q24 8th switching element, D21 5th return diode, D22 6th return diode, D23 7th return diode, D24 8th return diode, 26 DC-AC converter, 40 systems.

Claims (6)

A reactor connected to a DC power supply;
A first inverter circuit that converts a DC voltage input through the reactor to an AC voltage while boosting the DC voltage;
A transformer for transmitting output power of the first inverter circuit provided on the primary side to the secondary side;
A second inverter circuit which is provided on the secondary side of the transformer and converts AC power output from the first inverter circuit into DC power;
A short-circuit switch for short-circuiting both ends of the reactor;
A power conversion device comprising: In the first inverter circuit, a first leg in which a first switching element and a second switching element are connected in series, and a second leg in which a third switching element and a fourth switching element are connected in series are connected in parallel. Including a full-bridge circuit
The power converter is
A controller that complementarily drives the first switching element and the fourth switching element, and the second switching element and the third switching element;
The control unit, when operating the first inverter circuit, provides a period for storing energy in the reactor by controlling all of the first to fourth switching elements to an on state. The power converter according to 1. DC power output from the second inverter circuit is converted into AC power and supplied to an AC power supply or an AC load, or AC power supplied from an AC power supply is converted into DC power and supplied to the second inverter circuit A DC-AC converter that
The control unit controls all of the first switching element to the fourth switching element to be in an OFF state and controls the short-circuit switch to be in an ON state when a load visible from the AC side of the DC-AC converter is lower than a predetermined value. The power conversion device according to claim 2, wherein: A capacitor provided in parallel on the DC side of the second inverter circuit;
The control unit controls the short-circuit switch to an on state when the power converter is activated, and controls the short-circuit switch to an off state when a voltage of the capacitor exceeds a set value. The power converter according to 2 or 3.   The said control part raises the duty ratio of the said 1st switching element-the said 4th switching element according to the voltage rise of the said capacitor | condenser at the time of starting of the said power converter device. Power conversion device.   The short-circuit switch blocks current from the DC power supply side terminal of the reactor to the first inverter circuit side terminal, and drives current from the first inverter circuit side terminal to the DC power supply side terminal. 6. The power conversion device according to claim 1, wherein the power conversion device is a reverse blocking switch that is turned on or off according to a signal.

Images